The present invention relates generally to storage systems and, more particularly, to a method and an apparatus to support determining the unit size of storage area.
Recently, the use of thin provisioning has been popularized for storage systems. The thin provisioning technique can realize efficient use of storage area as well as reduction of management cost relating to the storage systems. With the thin provisioning, a storage system provides virtual volumes as storage areas to store data for computers. The storage system allocates and assigns physical areas to only locations having write access of the computers. Consequently, the total amount of used physical areas can be smaller than the total amount of virtual areas shown to the computers. The thin provisioning technique is disclosed, for example, in US2004/0162958, the entire disclosure of which is incorporated herein by reference.
In the above allocation and assignation, a “page” or a “chunk” is used as a unit for the allocation and assignation of storage area. Choosing the size of the chunk brings a trade-off between access performance and efficiency of the physical area usage. For example, a small size (i.e., small unit) provides high efficiency because any unused part of the assigned chunk will be relatively small, while the performance for sequential access is smaller than the performance involving a large size chunk because the frequency and total overhead of solving relation between the virtual area and the physical area can be large in the case of the small unit. Therefore the size of chunk should be selected with consideration for the trade-off regarding expected performance and expected efficiency. The performance and efficiency depend on usage (i.e., access pattern) of data stored in the volume. The usage can be different for each data (i.e., each location) in the volume.